I Need Help With This Question On Roof Framing

Michaeljp86

Im studying for my builders license and in the study guide I bought there is a question that had me thinking. I figured it out but I would like to know how the pros do it and if you would do it the same as me. The study guide didnt cover this at all but they have a question on it in the practice questions.

A 28x28 foot building has a 12" overhang. If the roof has a 4/12 pitch, what is the height of the roof rise at the heighest point?

a. 3feet
b. 4feet
c. 5feet
d. 6feet



I came up with 5 feet. 28 divided by 2 =14+1=15, 15x4=60, 60divided by 12=5

Is this the only way to do it or do you guys have a fast way to figure it out?

Second Look

You'll probably eventually memorize the roof pitches so you know that a 4/12 roof rises a third of a foot for every foot of run. Then when you get the 15 foot number, you just divide by 3.

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Jeff (socal)

You need to calculate the rise using the pathagorean theorem.
Formula of right triangle..a2+b2=c2
4feet- 8inch should be your rise for this roof slope with a run of 14.

Bradracer18

You can't really use the Pythagorean theorem, as you only know 1 side and 1 angle.

Just think of it.....you have to go over(run) of 15 feet....and it goes up 4" per every 1 foot. So, take the 15 x 4......= 60"......which is 5 foot.

Now, that you have that 5 foot, you could figure out the last slope using Pythagorean theorem

skyhook

The run is 14' (28 divided by 2) 4' plus 4" for every additional foot. 4' 8" is the rise as Jeff stated.

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tcleve4911

Bradracer is correct since the run is actually 15' not 14'.
That is the easiest way I've found also. 4/12 pitch means 4" of rise for every foot of run. That is 4" x 15 = 60" = 5'-0"

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Bradracer18

Yep, that seems to be the easiest way...and you guys are forgetting the extra foot on each side.....either way, I suppose you are explaining how to do it.

For this particular situation, I know that 60" is correct....I actually drew it up, to make sure....haha

Joe Carola

The question is wrong and misleading so are the answers to choose from. The run is not 15', the run is 14' to the plate. The overhang has nothing to do with the height of the ridge. You also need the size of the rafter to figure out the height.

The exact ridge height using run from outside of top plate:

Run - 1/2 ridge thickness x pitch + H.A.P. cut (Height above Plate) = Ridge Height

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Joe Carola

skyhook

the extra foot is overhange, the span is 28' .

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Bradracer18

I agree, and disagree. I agree, in that I understand how they are......but I disagree in how "we" are finding them.....

If you are using some sort of triangle method(pyth) then you would have to go out to the furthest point(12" past the top plate).

And, seens how they don't have more exact answers....I'm betting this is the way "they" want you do to it.

Joe Carola

If they want the run to be from the fascia at 15' and want just a simple triangle, then the rise would be 60". But that is 100% wrong as to where the height of the ridge would be. That's why the question and answers are misleading and wrong.

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Joe Carola

skyhook

4'8"

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woodmagman

You are doing this correct, now what is the line length of the hip for a building of the same dimensions including overhang and a 1.5" fasica and ridge are being used.....

go do it

56"

Michaeljp86

Joe, this is what really screwed me up, I was thinking the same way. I hate this question because of it. I decided the only way fo figure it would be like if they used a truss with the bottom chord extending over the top plate to for a sofit.

hrscammisa

Never seen them count the over hang its from the plt

KentWhitten

It's the question that is the problem. Everyone here can interpret in different ways.

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Joe Carola

The question is asking the roof rise at the highest point. I don't see any other way of interpreting that then the top of the ridge.

The problem is also in the answers they give to you.

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Joe Carola

KentWhitten

Not what I meant and it's obvious others are interpreting it differently so don't shake your head about it. The interpretation I'm talking about is where it STARTS, not ends.

If they made the question a little clearer, we wouldn't be arguing about this. It's dumb without the proper wording.

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Joe Carola

Not shaking my head over anything. or arguing over anything. So relax.

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